A guy who is closely related to you, who pisses you off, be it older or younger. Brothers may lurk around your room or even threaten to kill you. Many cases have shown that brothers are douchebags.
You: Hello, brother! How is this fine day?
Brother: Go fuck yourself.
You: .. wh- what?
Brother: I'm going to slit your throat.
You: No you're not
Brother: IM GOING TO MOTHERFUCKING KILL YOU!